TCCoA Forums banner

1 - 20 of 44 Posts

·
Registered
Joined
·
215 Posts
Discussion Starter · #1 ·
We currently have a 2 piece FN10 shaft in the MN12, with a rebuilt MN12 cast iron differential, Richmond Elite 3.73:1, Traction Lick with the Cobra carbon clutches.
Shortly, we are swapping in a 97 Mark engine. We have harvested a second 2 piece aluminum shaft from that car.

We want to go fast, and know we need a better shaft as we get faster.

My guy that did the gearbox work is a lifelong ford mechanic and his advice was to get the shaft balanced.

My question is when speaking of drive shafts in a car and balancing, what is "Dynamic Balancing"
And:
Assuming there is other than "Dynamic Balancing", like maybe "static balancing" what is the difference?

How much should I expect to pay for either? We have a local vendor, Gilbert Shaft that adverts the dynamic balancing but has no website info.

Thanks
 

·
Super Moderator
Joined
·
11,265 Posts
I would not waste the cash to have a stock one rebalanced; thats throwing money away.
They are two pieces of thin sheetmetal with rtv between the sheets.

That's the first thing I replace, lol.
 
  • Like
Reactions: Trunk Monkey

·
Registered
Joined
·
215 Posts
Discussion Starter · #3 ·
Hi Grog,

When we started this,we spotted the crappy stock MN12 shaft in our search for an elusive but awful driveline "clunk".
We changed that thing to a 94+ FN10 shaft when we did the differential and IRS work.
Lacking the cash for an aftermarket and unable to locate a 1993 Mark shaft, it was the best option available.
I know we have to upgrade it at some point but right now I have two that are in excellent condition.
They certainly appear far superior to the MN12 shaft, and the car likes it.

The elusive clunk remained unfound until I got the converter out of the car and shook it. Sounds like a bad rear u-joint and a lot of backlash.

Thanks, if you know of anyone with a shaft or insight on balancing, I would really be appreciative.
 

·
Super Moderator
Joined
·
8,006 Posts
You can’t rebalance the factory 2-piece shaft. It is held together with rubber, and rebalancing requires welding weights onto the shaft, which will damage the rubber due to the heat. The 2 piece MarkVIII shaft is better than the MN12 shaft, but neither one is at all suited to sustained high speeds. The rubber will deflect at high speeds, causing vibration, and that vibration will crack the tail shaft housing on the transmission. If you want to go fast, you need a good quality aluminum one piece driveshaft, which will probably cost you in the neighborhood of $600. If you can’t afford that, then work more and save more money, or be content with around 120mph top speed. Or you could run a 2.47 rear gear and have the car be abysmally slow off the line. I’m all about low budget projects, but part of a low budget project involves knowing where to spend the money and where you can save it, and unfortunately for our cars, if you are looking for top speed, the driveshaft is one of those areas where you will have to spend some money.
 

·
Registered
Joined
·
215 Posts
Discussion Starter · #5 ·
I understand your point and am wholly in agreement.
We are just getting started and need to walk before we fly, therefore a top speed of 120mph is just fine.

I have done a tremendous amount of work to the car, pretty much disassembled in entirety, and improved to the best of my ability.

What I am saying is, to get the car shaken out, the two piece is fine. I was not shy regarding my steering mods, suspension mods, transmission mods, differential mods, chassis mods, etc.

I need to get the car back together and shake it down; It needs 4 wheel alignment, a complete tune and any possible NVA issue resolved for the most part. That should give me time to save up. I am permanently disabled with a pancreas problem that is serious I guess. Money does not come to me easily.

Thanks for your input.

Does anyone know?
If not I can just call and ask I guess.

RD

RD
 

·
Super Moderator
Joined
·
8,006 Posts
Does anyone know what? Call and ask who what? If you are not looking for the top speed just yet, then run the MarkVIII shaft. If you want to go faster than that will allow, then you will need to spend the money on a new shaft.
 
  • Like
Reactions: Trunk Monkey

·
The Parts Guy
Joined
·
7,682 Posts
What driveshaft shop is offering a static balance? I don't know of any reputable driveshaft shop that wouldn't dynamic balance a driveshaft. The big deal, especially if you're planning to run land speed events, is the rpm that your shop will spin it to.
 

·
Super Moderator
Joined
·
11,265 Posts
Brand new 3.5" Aluminum shafts from PST are ~$549; I own 3 and have not had any issues. They even gave me the Group buy price like 10 years later. There may be a tccoa discount; I'd ask.:)

The only person to break one of these let the loop near the gastank rub on it, it acted like a parting tool and cut it off. :)
 
  • Like
Reactions: CDsDontBurn

·
The Parts Guy
Joined
·
7,682 Posts
I've run the same PST shaft for 16 years now with no complaints either. I've spun it up to 7k rpm (at the driveshaft) numerous times as well.
 

·
Super Moderator
Joined
·
11,265 Posts
Two of the stock driveshafts were completely trashed. One shook like a moracca. and the second spun inside on hard shifts. :)

I guess I've hit 7k on the driveshaft; I drive bad , lol.
wonder if a gps would hold up in court if they siezed it, or maybe a datalog...
 

·
Administrator
Joined
·
13,709 Posts
As has been suggested; I agree, on a budget get a Mark VIII shaft. Otherwise get the Dynotech 3.5" period. I paid $360 for mine in 2007. I just checked, SCP has doubled the asking price in the 14 years since then. (OMG Where does the time go!?)

The 3.5" shaft from them is now $619. Talk about getting the shaft!


I'm sure you can still get it for substantially less by buying it directly from Dynotech.


DSS is another option: The Driveshaft Shop | Home Page - Driveshaft Shop

I ordered my half-shafts from DSS.
 

·
Registered
1991 Mercury Cougar LS 5.0 in restoration
Joined
·
784 Posts
There is a driveshaft shop in town here that I plan to ask when I'm ready to put the car together. Any chance there is a shop within a reasonable distance that could build one to spec for you? Not sure if it would cost more or not, but just might be cheaper than $600????
 

·
Registered
Joined
·
65 Posts
I got a quote for an aluminum shaft from a driveshaft shop where I live, and he told me 1400 Canadian plus 12% tax for a total of 1568 dollars.
That is 1300 American dollars.
I am just going to keep using the stock one with my 3:73's. If we go 25 mph over the limit up here, we get impounded for 7 -30 days and excessive speeding tickets and ridiculous fines. So on our fastest hwy, 95 mph would be impoundable, and I would never go that fast in my normal driving on that highway.
 

·
Registered
Joined
·
215 Posts
Discussion Starter · #14 ·
Thank you all very much for your input.

There are aftermarket shaft balancing techniques that requre no welding. They are Mercury vessels that can do this with a steel band. I am going to call them.

Does anyone know what? Call and ask who what? If you are not looking for the top speed just yet, then run the MarkVIII shaft. If you want to go faster than that will allow, then you will need to spend the money on a new shaft.
To your question, the first one.

What is the difference between static balancing and dynamic balancing?

And the latter,
I will call the vendor, Gilbert Shaft in Manchester NH. They also offer build services. Back in my day, I was a regular customer by way of my 1970 440 Charger, but not for balancing. That car a distressing habit of crinkling a shaft about every year. On the rare occasion that car actually hooked, it caused damage.

And again, I really appreciate the input,all of it.
 

·
Super Moderator
Joined
·
8,006 Posts
Any balancing on a driveshaft is going to be dynamic balancing. The idea is to spin the driveshaft to simulate its movement in the car, and make sure that it spins true. Static balancing is basically just making sure the center of gravity is on the axis of spin. Static balancing is like using a bubble balancer on a tire.

The problem with balancing a driveshaft that is held together with rubber is that the forces exerted on the shaft cause deflection in the rubber, which changes the forces and therefore the balancing. The 2-piece MarkVIII shaft was made to absorb noise and vibration at normal speeds. It was not made for sustained high rpm. It cannot be adapted to sustained high rpm. It cannot be properly balanced, and any balancing done to it will not help with high speed stability because the deflection in the rubber will not be predictable, and will result in vibrations. This is why everyone is saying that spending any money on a 2-piece driveshaft is a waste. The only money you should possibly spend on that driveshaft would be to buy some new u-joints, and even that would only be if there is play or tight spots in the joints. Otherwise, bolt the thing in and forget about it until you are ready for real speed. You really are overthinking this.
 
  • Like
Reactions: racecougar

·
The Parts Guy
Joined
·
7,682 Posts
Any balancing on a driveshaft is going to be dynamic balancing. The idea is to spin the driveshaft to simulate its movement in the car, and make sure that it spins true. Static balancing is basically just making sure the center of gravity is on the axis of spin. Static balancing is like using a bubble balancer on a tire.

The problem with balancing a driveshaft that is held together with rubber is that the forces exerted on the shaft cause deflection in the rubber, which changes the forces and therefore the balancing. The 2-piece MarkVIII shaft was made to absorb noise and vibration at normal speeds. It was not made for sustained high rpm. It cannot be adapted to sustained high rpm. It cannot be properly balanced, and any balancing done to it will not help with high speed stability because the deflection in the rubber will not be predictable, and will result in vibrations. This is why everyone is saying that spending any money on a 2-piece driveshaft is a waste. The only money you should possibly spend on that driveshaft would be to buy some new u-joints, and even that would only be if there is play or tight spots in the joints. Otherwise, bolt the thing in and forget about it until you are ready for real speed. You really are overthinking this.
AMEN!
 

·
Registered
Joined
·
13 Posts
As has been suggested; I agree, on a budget get a Mark VIII shaft. Otherwise get the Dynotech 3.5" period. I paid $360 for mine in 2007. I just checked, SCP has doubled the asking price in the 14 years since then. (OMG Where does the time go!?)

The 3.5" shaft from them is now $619. Talk about getting the shaft!


I'm sure you can still get it for substantially less by buying it directly from Dynotech.


DSS is another option: The Driveshaft Shop | Home Page - Driveshaft Shop

I ordered my half-shafts from DSS.
Surprisingly the dynotech shafts are about the same price direct as SCP sells them for.
I just ordered a 4 inch aluminum shaft and it was $700 shipped to me.
 

·
Administrator
Joined
·
13,709 Posts
Surprisingly the dynotech shafts are about the same price direct as SCP sells them for.
I just ordered a 4 inch aluminum shaft and it was $700 shipped to me.
4" is overkill. Be careful installing it. Some have had clearance issues with that size. Mine is the 3.5" version.
 
  • Like
Reactions: CDsDontBurn
1 - 20 of 44 Posts
Top